EP2981570B1 - Welded structural link between a high-performance thermoplastic matrix composite material and an elastomer by functionalisation in powder mode - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to the field of structural chemical assemblies of different materials, and more specifically the assembly of elastomeric materials with thermoplastic materials.

Very generally, the term "thermoplastic material" refers to any material comprising a certain percentage of thermoplastic material constituting a matrix, whether it is a material consisting solely of thermoplastic material or, for example, of a continuous fiber composite material. and thermoplastic matrix.

The invention finds, for example, a particular application in the context of the manufacture of propellant stages of powder rockets, to achieve the connection of the reservoir with the skirts.

BACKGROUND OF THE INVENTION - PRIOR ART

Welding assembly of two high performance thermoplastic matrix composite materials generally employs known assembly methods. Moreover, in order to bring the assembly area to the desired temperature, it is possible to implement several known principles of heating such as heating by hot gas (oven, autoclave), by vibration (ultrasound, rotation), by induction, resistance, etc ... This type of assembly is described in particular in the book of Michael J. Troughton entitled "Handbook of plastics joining" (Plastics Design Library). ISBN: 978-1-884207-17-4 .

Conversely, there is, to date, no known means for performing the welding assembly of a thermoplastic matrix composite material and an elastomeric type material. This absence seems to stem from the fact that, in so far as elastomers do not have the property of reversibly passing from the solid state to the molten state, an assembly technique requiring heating of the materials to be assembled, at least at the level of the assembly zone, does not seem obvious to the man of the job.

For some applications, the known assembly techniques for assembling a thermoplastic material element with a polymer material element do not have the required qualities, in terms of mechanical strength in particular.

This is the case for example, as schematically illustrates the figure 1 , for assembling a ferrule 11 (made of metallic material or composite with a thermoplastic or thermosetting matrix) on a reservoir 12 made of thermoplastic matrix composite to constitute a propellant stage of a powder launcher, or a reservoir of consumer gas.

Indeed, this assembly requires the insertion of a layer 13 of elastomeric material within the bond, the layer of elastomeric material having the role of absorbing significant differential deformations that appear between the two structures. As a result, the insertion of this layer 13 of interlayer elastomeric material requires the assembly of this layer on the two composite material elements constituted by the reservoir 12 and the shell 11, this assembly necessarily having to be of high mechanical quality, makes constraints on the assembly.

However, in terms of mechanical strength a welded connection is generally greater than a bonded bond. Indeed, after welding, there is no differentiated interface between the two assembled parts, because of the diffusion of the molecules from one part to another, whereas in the case of a bonding, there is as many interfaces as layers necessary for the creation of the bond, layers among which are mainly in addition to the adhesive layer itself, the adhesion primers, as well as the treatments applied to the surfaces to be assembled.

Moreover, in the case of welding, the constraints generated by the preparation of the surfaces before assembly and by their protection against pollution are also eliminated, these operations being necessary, even imperative, in the case of a bonding assembly.

The document DE 27 46 544 A1 discloses a method for making a welded structural connection between a polyvinyl chloride and an elastomeric material comprising incorporating a polyethylene powder into the elastomer.

The document GB 1 579 433 A describes a method for producing a welded structural connection between a nylon-reinforced poly (vinyl chloride) and an elastomer, comprising a first operation of functionalization of the elastomeric material, the functionalization being carried out by painting the surface of the elastomer material with a solution comprising ethylene-vinyl acetate, and a second welding operation proper, during which the (radio frequency) welding of the nylon-reinforced poly (vinyl chloride) to the functionalized layer of the elastomeric material is carried out.

The document EP 0 440 410 A2 discloses a method for joining a fiber reinforced pastic material to a rubber in which an adhesive and a heat generating material are provided between the plastic and the vulcanized rubber and the temperature is raised to bond the plastic material to the rubber.

The document JP H 06 134870 A describes the connection between a rubber and a composite resin element by induction heating.

PRESENTATION OF THE INVENTION

An object of the invention is to provide a solution for performing the structural assembly by welding a thermoplastic material and an elastomeric material, the focus being on these two families of materials.

• une première opération de fonctionnalisation du matériau élastomère par incorporation dans le matériau élastomère cru d'une proportion donnée de poudre d'un matériau thermoplastique, la fonctionnalisation étant réalisée par réalisation d'une couche mince de matériau élastomère cru intégrant une proportion de poudre de matériau thermoplastique et fusion de ladite couche avec la couche principal de matériau élastomère durant l'opération de vulcanisation sous pression dudit matériau élastomère;
• une seconde opération de soudage proprement dit, durant laquelle on réalise le soudage du matériau composite thermoplastique à la couche fonctionnalisée du matériau élastomère.

To this end, the subject of the invention is a method for producing a welded structural connection between a thermoplastic matrix composite material and an elastomer, said method comprising the following operations:

• a first operation of functionalization of the elastomeric material by incorporation in the green elastomeric material of a given proportion of powder of a thermoplastic material, the functionalization being carried out by producing a thin layer of raw elastomer material incorporating a proportion of powder of material thermoplastic and melting said layer with the main layer of elastomeric material during the pressure vulcanization operation of said elastomeric material;
• a second welding operation itself, during which the thermoplastic composite material is welded to the functionalized layer of the elastomeric material.

According to various particular provisions, which can be considered in conjunction, the method according to the invention may furthermore have the following characteristics.

• une étape préliminaire A) de nettoyage des différentes parties du moule de vulcanisation utilisé;
• une première étape B) durant laquelle on prépare une couche fine d'élastomère cru pré-fonctionnalisée en incorporant, de manière homogène à cette couche d'élastomère une proportion donnée de poudre de matériau thermoplastique;
• une deuxième étape C) durant laquelle on applique la couche fine d'élastomère cru pré-fonctionnalisée à la surface du matériau élastomère
• une troisième étape D) durant laquelle on procède à la vulcanisation sous-pression du matériau élastomère; la pression appliquée étant déterminée de façon à ce que la couche fine d'élastomère cru pré-fonctionnalisée s'incorpore, au moins en surface, à la couche principale de matériau élastomère durant le processus de vulcanisation.

According to one particular arrangement, the operation of producing the functionalized elastomer itself comprises several steps:

• a preliminary step A) of cleaning the different parts of the vulcanization mold used;
• a first step B) during which a thin layer of pre-functionalized raw elastomer is prepared by homogeneously incorporating into this elastomer layer a given proportion of powder of thermoplastic material;
• a second step C) during which the thin layer of pre-functionalized raw elastomer is applied to the surface of the elastomeric material
• a third step D) during which the underpressure vulcanization of the elastomeric material is carried out; the pressure applied being determined so that the thin layer of pre-functionalized raw elastomer is incorporated, at least on the surface, with the main layer of elastomeric material during the vulcanization process.

According to another particular arrangement, the thermoplastic material incorporated in the thin layer of elastomeric material is selected so as to be both welded to the thermoplastic material forming the matrix of the composite material and to have good compatibility with the elastomeric material.

According to a variant of the preceding arrangement, the thermoplastic material incorporated in the thin layer of elastomeric material is identical to the thermoplastic material forming the matrix of the composite material.

According to another variant of the same previous provision, the composite material being a carbon / polyetheretherketone composite and the elastomeric material being of HNBR type, the thermoplastic material incorporated in the thin layer of elastomeric material is a polyetherimide.

According to another particular provision, the thermoplastic material is incorporated into the elastomeric material in the form of particles with a diameter of between 20 .mu.m and 60 .mu.m, in a proportion of between 10% and 25% of the mixture by mass.

According to another particular arrangement, the welding operation II) consists in heating the contact surfaces of the two materials to be welded by interposing between these two surfaces a wire cloth which acts as a heating resistor, the wire mesh being itself impregnated with thermoplastic material.

According to a variant of the preceding arrangement, the welding operation is preceded by a preliminary operation I) of preparing the surfaces of the materials to be assembled, this operation possibly consisting, depending on the state of these surfaces, either in a simple degreasing at using a suitable solvent, or by fine sanding the functionalized surface of the elastomeric element, followed by cleaning the surfaces with the same solvent.

1. a) une première opération de mise en place, sur le plateau inférieur du moule de vulcanisation, des éléments suivants:
   • deux couches superposées de tissu de verre téflonné;
   • un pli de matériau élastomère cru dans lequel a été incorporé de la poudre de polyétherimide;
   • les plis du matériau élastomère cru non vulcanisé;
   • un jeu de cales de bordurage;
   • deux couches superposées de tissu de verre téflonné; l'ensemble étant coiffé par le plateau supérieur du moule de vulcanisation;
2. b) une deuxième opération de mise en place de l'empilement réalisé sur le plateau d'une presse chauffante préchauffée à une température θ₂ de 140°C;
3. c) une troisième opération de pressage à chaud de l'empilement, durant laquelle on appliquer le cycle de pressage nominal adapté à l'élastomère considéré.
4. d) une quatrième opération durant laquelle on retire le moule de la presse alors que celle-ci maintient la température θ₂ de 140°C, on démoule l'élastomère fonctionnalisé et on laisse refroidir celui-ci à température ambiante.

According to another particular arrangement, the composite material being a carbon / polyetheretherketone composite and the elastomeric material being of the HNBR type, the actual development step C) of the functionalized elastomer comprises the following operations:

1. a) a first operation of placing, on the bottom plate of the vulcanization mold, the following elements:
   • two superimposed layers of teflon glass cloth;
   • a ply of raw elastomeric material in which polyetherimide powder has been incorporated;
   • the folds of the unvulcanized raw elastomeric material;
   • a set of boarding wedges;
   • two superimposed layers of teflon glass cloth; the assembly being capped by the upper plate of the vulcanization mold;
2. b) a second operation of placing the stack formed on the plate of a heating press preheated to a temperature θ ₂ of 140 ° C;
3. c) a third hot pressing operation of the stack, during which the nominal pressing cycle adapted to the elastomer considered is applied.
4. d) a fourth operation during which the mold is removed from the press while the latter maintains the temperature θ ₂ of 140 ° C, it is unmolded the functionalized elastomer and allowed to cool to room temperature.

• une phase de montée progressive en température jusqu'à une température haute θ₁ de 230°C avec un gradient de 2.5°C/min,
• une phase de maintien à la température θ₁ durant 10 minutes,
• une phase de descente en température jusqu'à la température θ₂ de 140°C selon un gradient en 2.5°C/min.

According to a variant of the preceding arrangement, the pressing cycle of the third operation comprises:

• a phase of gradual rise in temperature to a high temperature θ ₁ of 230 ° C. with a gradient of 2.5 ° C./min,
• a maintenance phase at the temperature θ ₁ for 10 minutes,
• a phase of descent in temperature up to the temperature θ ₂ of 140 ° C according to a gradient in 2.5 ° C / min.

1. a) Une première étape de mise en place durant laquelle on dispose principalement, dans l'ordre, sur une plaque de matériau isolant thermique, les éléments suivants:
   • un premier film en polyimide résistant à la chaleur,
   • le matériau élastomère fonctionnalisé,
   • un premier film de polyétherimide,
   • une toile métallique préimprégnée de polyétherimide,
   • un second film de polyétherimide,
   • le matériau composite thermoplastique,
   • un second film en polyimide,
   • une couche d'isolant thermique,
   • un tissu de verre;
2. b) Une deuxième étape durant laquelle on réalise une vessie sous vide avec un film de polyimide disposé de façon à laisser la toile métallique ressortir, l'étanchéité de ladite vessie étant assurée au moyen de mastic à haute température.
3. c) Une troisième étape durant laquelle on met sous vide la vessie, on connecte un bloc d'alimentation électrique sur la toile métallique et on applique différentes valeurs d'intensité suivant un cycle approprié.
4. d) Une quatrième étape durant laquelle on retire le film de polyimide servant de bâche à vide et on démonte l'empilement.

According to another particular arrangement, the composite material being a carbon / polyetheretherketone composite and the elastomeric material being of the HNBR type, the welding operation II) itself comprises the following steps:

1. a) A first implementation step during which the following elements are mainly arranged, in order, on a plate of thermal insulating material:
   • a first heat-resistant polyimide film,
   • the functionalized elastomeric material,
   • a first polyetherimide film,
   • a metal cloth pre-impregnated with polyetherimide,
   • a second polyetherimide film,
   • the thermoplastic composite material,
   • a second polyimide film,
   • a layer of thermal insulation,
   • a glass cloth;
2. b) A second step during which a vacuum bladder is made with a polyimide film arranged so as to let the wire cloth out, the sealing of said bladder being ensured by means of high temperature mastic.
3. c) A third step during which the bladder is evacuated, a power supply unit is connected to the wire mesh and different intensity values are applied in a suitable cycle.
4. d) A fourth step during which the polyimide film used as a vacuum cover is removed and the stack is removed.

According to a variant of the preceding arrangement, during the third step, a current of 15.6 amps is applied to the wire mesh for 200 seconds and then a current of 10 amperes for 100 seconds.

DESCRIPTION OF THE FIGURES

• la figure1, une illustration schématique d'un exemple de structure pour laquelle l'assemblage par soudage des différents éléments semble particulièrement adapté, du fait des contraintes mécaniques imposées à cet assemblage;
• la figure 2, une illustration d'un exemple de mise en oeuvre de l'étape de fonctionnalisation de l'élastomère du procédé selon l'invention;
• la figure 3, une illustration d'un exemple de mise en oeuvre de l'opération de soudage selon l'invention.

The characteristics and advantages of the invention will be better appreciated thanks to the following description, which is based on the appended figures which show:

• the figure 1 , a schematic illustration of an example of a structure for which the assembly by welding of the various elements seems particularly suitable, because of the mechanical stresses imposed on this assembly;
• the figure 2 an illustration of an exemplary implementation of the functionalization step of the elastomer of the process according to the invention;
• the figure 3 , an illustration of an example of implementation of the welding operation according to the invention.

DETAILED DESCRIPTION

The principle of the method according to the invention consists mainly in the implementation before the actual welding, an operation of preparation of the elastomeric material. This operation consists of assembling in the "green elastomer" stage, that is to say non-vulcanized stage, two distinct layers of elastomer material, a first layer, or main layer, of homogeneous raw elastomeric material, and a second layer called "pre-vulcanized" layer. -fonctionnalisée ". The functionalization operation here consists in modifying the surface, or the core itself, of the elastomer in order to give it the properties necessary to be able to weld it to the thermoplastic composite material. By "functionalizing the elastomeric material" is meant to modify the composition of the surface layers of this material by incorporating a thermoplastic material therein.

For this purpose, to produce the first so-called "functionalized" layer, a proportion of powder of a thermoplastic material having both a compatibility with the elastomeric material and being welded to the matrix of the thermoplastic composite material to which we want to assemble the elastomeric material considered.

Compatibility between the elastomeric material and the thermoplastic material forming the powder incorporated in this material mainly means, in this case, a physicochemical compatibility between the two materials. This compatibility results in a possible interaction between the thermoplastic material of the incorporated powder and the elastomer in which this powder is incorporated, an interaction which a person skilled in the field of plastics chemistry knows to characterize by specific criteria, of a rather chemical: wettability, interdiffusion between materials, chemical bonding.

However, it is also interested in a compatibility of implementation between the different materials (physical compatibility), particularly with regard to the need to be able to vulcanize the temperature of the elastomer thus functionalized without deteriorating the thermoplastic material incorporated in the form. of powder.

1. A) une étape préalable de nettoyage des différentes parties du moule de vulcanisation, nettoyage réalisé, par exemple, au Méthyléthylcétone (ou MEC).
2. B) une première étape durant laquelle on prépare une couche fine de matériau élastomère cru, pré-fonctionnalisée en incorporant, de manière homogène à cette couche d'élastomère une proportion donnée de poudre de matériau thermoplastique;

According to the invention, the elaboration process of the functionalized elastomer comprises several steps:

1. A) a preliminary cleaning step of the various parts of the vulcanization mold, cleaning carried out, for example, with methyl ethyl ketone (or MEC).
2. B) a first step during which a thin layer of pre-functionalized elastomeric material is prepared by homogeneously incorporating into this elastomer layer a given proportion of powder of thermoplastic material;

According to the invention the proportion of powder is determined by carrying out mechanical tests on peel test pieces, by adjusting this proportion so as to obtain the desired value of peel strength, value equal to at least 20 N / mm.

Moreover, the particle size of the powder is chosen to facilitate mixing with the elastomer.

• C) une deuxième étape durant laquelle on applique la couche d'élastomère cru pré-fonctionnalisée à la surface du matériau élastomère cru à assembler au matériau composite thermoplastique et,
• D) une troisième étape durant laquelle on procède à la vulcanisation sous-pression du matériau élastomère. Selon l'invention, la pression appliquée est déterminée de façon à ce que les deux couches de matériau élastomère fusionnent en surface durant le processus de vulcanisation.

According to the invention also, the various constituents of the raw elastomer, consisting for example of gum base oil and silica fillers, and the proportion of powder of thermoplastic material are mixed in a closed mixer of Werner type. The peroxide vulcanizing agent is then added to an open mixer. The last step is to calender the functionalized raw elastomer thus obtained, so as to achieve the thin layer of the desired thickness.

• C) a second step during which the pre-functionalized raw elastomer layer is applied to the surface of the raw elastomer material to be assembled to the thermoplastic composite material and,
• D) a third step during which the underpressure vulcanization of the elastomeric material is carried out. According to the invention, the pressure applied is determined so that the two layers of elastomeric material fuse on the surface during the vulcanization process.

A vulcanized functionalized elastomer is obtained comprising a conventional elastomer base covered with a thin functionalized elastomer layer, for example a layer 1 mm thick.

1. a) Une première opération de mise en place, sur le plateau inférieur 21 du moule de vulcanisation, des éléments nécessaires à la mise en oeuvre de la fonctionnalisation du matériau élastomère, à savoir, dans l'ordre et comme illustré par la figure 2 :
   • deux couches superposées 22 et 23 de tissu de verre téflonné, dont le rôle consiste à permettre le démoulage de l'élastomère après polymérisation;
   • La couche d'élastomère cru 24 dans lequel a été incorporé de la poudre de Polyétherimide (ou PEI). La poudre choisie est une poudre de PEI, de l'Ultem® 1000 par exemple, qui présente un diamètre médian compris entre 20µm et 60µm, un diamètre de 45µm par exemple. La proportion de poudre incorporée a quant à elle une valeur comprise entre 10% et 25% du mélange global en masse, une valeur sensiblement égale à 20% par exemple.
   • les plis du matériau élastomère (HNBR) cru 25 (non vulcanisé), à fonctionnaliser,
   • un jeu de cales de bordurage 26, 27, des cales en acier inoxydable type 304L par exemple,
   • deux couches superposées 28 et 29 de tissu de verre téflonné, assurant un rôle analogue à celui assuré par les couches 22 et 23.
   
   Après mise en place, l'ensemble est coiffé par le plateau supérieur 211 du moule de vulcanisation de sorte que tous les éléments listés précédemment sont placés entre le plateau inférieur 21 et le plateau supérieur 211 du moule;
2. b) une deuxième opération de mise en place de l'empilement réalisé sur le plateau d'une presse chauffante préchauffée à une température θ₂ de 140°C;
3. c) une troisième opération de pressage à chaud de l'empilement, durant laquelle on appliquer le cycle de pressage nominal adapté à l'élastomère considéré, ce cycle comportant :
   • une phase de montée progressive en température jusqu'à une température haute θ₁ (230°C en 2.5°C/min),
   • une phase de maintien à la température θ₁ (palier de 10 minutes à 230°C),
   • une phase de descente en température jusqu'à la température θ₂ (140°C en 2.5°C/min);
4. d) une quatrième opération durant laquelle on retire le moule de la presse alors que celle-ci maintient la température θ₂ (140°C), on démoule l'élastomère fonctionnalisé et on laisse refroidir celui-ci à température ambiante.

Thus, for example, in a particular embodiment of the invention, adapted more particularly to the welding of a polyetheretherketone (PEEK) matrix composite material and to a carbon fiber reinforcement (carbon / PEEK thermoplastic composite) with a elastomer of the hydrogenated nitrile rubber (hydrogenated butadiene-acrylonitrile) type, or Buna or HNBR (acronym for the English name ", hydrogenated nitrile butadiene rubber"), step C) of actual elaboration of the functionalized elastomer can itself include the following operations:

1. a) A first operation of placing, on the lower plate 21 of the vulcanization mold, elements necessary for the implementation of the functionalization of the elastomeric material, namely, in the order and as illustrated by FIG. figure 2 :
   • two superimposed layers 22 and 23 of teflon glass fabric, the function of which is to allow the demolding of the elastomer after polymerization;
   • The green elastomer layer 24 in which has been incorporated polyetherimide powder (or PEI). The powder chosen is a PEI powder, for example Ultem® 1000, which has a median diameter of between 20 μm and 60 μm, a diameter of 45 μm, for example. The proportion of powder incorporated has a value of between 10% and 25% of the total mixture by weight, a value substantially equal to 20% for example.
   • the folds of the raw elastomeric material (HNBR) 25 (unvulcanized), to be functionalized,
   • a set of shims 26, 27, wedges of stainless steel type 304L for example,
   • two superposed layers 28 and 29 of teflon glass fabric, ensuring a role similar to that provided by the layers 22 and 23.
   
   After placement, the assembly is capped by the upper plate 211 of the vulcanization mold so that all the elements listed above are placed between the lower plate 21 and the upper plate 211 of the mold;
2. b) a second operation of placing the stack formed on the plate of a heating press preheated to a temperature θ ₂ of 140 ° C;
3. c) a third heat-pressing operation of the stack, during which the nominal pressing cycle adapted to the considered elastomer is applied, this cycle comprising:
   • a phase of gradual rise in temperature to a high temperature θ ₁ (230 ° C. at 2.5 ° C./min),
   • a maintenance phase at the temperature θ ₁ (10 minutes stage at 230 ° C.),
   • a temperature descent phase up to the temperature θ ₂ (140 ° C. at 2.5 ° C./min);
4. d) a fourth operation during which the mold is removed from the press while the latter maintains the temperature θ ₂ (140 ° C), the functionalized elastomer is demolded and allowed to cool to room temperature.

Thus, as has been said above, a surface-functionalized vulcanized elastomer comprising a conventional elastomer base having a surface layer of functionalized elastomer 24 formed of a mixture of elastomer and thermoplastic material.

In a particular embodiment, the thermoplastic material used to perform the functionalization operation of the elastomer is chosen from the same material as that which constitutes the matrix of the composite material to which the elastomeric material is to be welded. It should be noted, however, that the thermoplastic material used may be different, especially to best meet the double requirement of good adhesion of the two thermoplastic materials (ie that of the composite material and that used for the functionalization of the elastomer) and good compatibility of the material used for the functionalization of the elastomer and the elastomeric material itself.

Once the polymer material has been functionalized, the process according to the invention continues with the actual welding step, an operation which, thanks to the functionalization of the polymer material, advantageously proceeds in a manner analogous to a welding operation of two pieces of material thermoplastic matrix composite. This operation can in particular be carried out by induction or by resistance.

It should be noted that advantageously, the welding operation is not subjected to any delay constraint to be achieved, unlike what is likely to occur for a bonding assembly. Insofar as the functionalized elastomeric material is vulcanized before assembly, the welding of the two materials can thus be carried out at the moment considered to be the most appropriate, a time that may be more or less distant in time from that of completion of the functionalization.

The resistance method consists in locally heating the interface between the composite material and the functionalized elastomer, to obtain a bond between the thermoplastic matrix of the composite material and the thermoplastic portion of the functionalized elastomer.

According to the invention, the welding step begins with a preliminary operation I) of preparing the surfaces to be assembled. According to the state of these surfaces the preparation may consist of a simple degreasing using a suitable solvent, ethanol for example, or a fine sanding of the functionalized surface of the elastomer element, with a 400 grit sandpaper Sic for example, followed by cleaning, using the same solvent, surfaces and in particular the sanded surface. By appropriate solvent is meant here a solvent of the fatty substances which by its nature or composition does not present any risk of causing a dissolution of the material itself.

It then continues with the actual welding operation II) of heating the contact surfaces of the two materials to be welded by interposing between these two surfaces a wire mesh which acts as a heating resistor; the operation being carried out under vacuum.

According to the invention, the wire cloth is itself impregnated with thermoplastic material, PEI for example.

1. a) Une première étape de mise en place durant laquelle, comme illustré par la figure 3, on dispose principalement, dans l'ordre, sur une plaque 31 de matériau isolant thermique, de NL FIH par exemple, les éléments suivants:
   • un premier film 32 en polyimide résistant à la chaleur, de préférence un film d'Upilex®, destiné à favoriser le désassemblage de l'ensemble après soudage,
   • le matériau élastomère fonctionnalisé 33,
   • un premier film 34 de polyétherimide (PEI), de type Ultem® 1000 par exemple,
   • une toile métallique 35 préimprégnée de PEI, par exemple une toile de référence 102083 fabriquée par la sté Gantois,
   • un second film 36 de polyétherimide (PEI),
   • le matériau composite thermoplastique 36 (C/PEEK) revêtu de PEI,
   • un second film 37 en polyimide Upilex destiné également à favoriser le désassemblage de l'ensemble après soudage,
   • une couche d'isolant thermique 38 (NL FIH),
   • un tissu de verre 311, de type E5555 par exemple, destiné à favoriser le drainage de l'air présent.
2. b) Une deuxième étape durant laquelle on réalise une vessie sous vide avec un film 312 de polyimide (Thermalimide) disposé de façon à laisser la toile métallique imprégnée de PEI ressortir ; l'étanchéité étant obtenue avec un mastic haute température A800 3G.
3. c) Une troisième étape durant laquelle on met sous vide la vessie 312 ainsi réalisée, on connecte un bloc d'alimentation électrique sur la toile métallique 35 et on applique différentes valeurs d'intensité suivant un cycle approprié: par exemple 15.6 ampères pendant 200 secondes puis 10 Ampères durant 100 secondes.
4. d) Une quatrième étape durant laquelle on retire le film de polyimide 312 servant de bâche à vide et on démonte l'empilement, de façon à récupérer l'assemblage élastomère-composite thermoplastique ainsi réalisé.

Thus, for example, in a particular embodiment of the invention, adapted more particularly to the welding of a composite material PEEK matrix and carbon fiber reinforcement (carbon / PEEK thermoplastic composite) with an elastomer HNBR type (Buna), the actual welding operation II) itself may comprise the following steps:

1. a) A first stage of implementation during which, as illustrated by the figure 3 , in order, on a plate 31 of thermal insulating material, NL FIH for example, the following elements are mainly arranged:
   • a first film 32 of heat-resistant polyimide, preferably an Upilex® film, intended to promote the disassembly of the assembly after welding,
   • the functionalized elastomeric material 33,
   • a first film 34 of polyetherimide (PEI), of the Ultem® 1000 type, for example ,
   • a wire pre-impregnated with PEI, for example a reference fabric 102083 manufactured by the Gantois firm,
   • a second film 36 of polyetherimide (PEI),
   • the thermoplastic composite material 36 (C / PEEK) coated with PEI,
   • a second film 37 of Upilex polyimide also intended to promote the disassembly of the assembly after welding,
   • a layer of thermal insulation 38 (NL FIH),
   • a glass fabric 311, type E5555 for example, intended to promote the drainage of the air present.
2. b) A second step during which a vacuum bladder is made with a film 312 of polyimide (Thermalimide) arranged so as to leave the PEI-impregnated wire cloth out; the seal being obtained with a high temperature sealant A800 3G.
3. c) A third step during which the bladder 312 thus made is evacuated, a power supply unit is connected to the wire mesh 35 and different intensity values are applied according to a suitable cycle: for example 15.6 amperes for 200 seconds then 10 amps for 100 seconds.
4. d) A fourth step during which the polyimide film 312 used as a vacuum tarpaulin is removed and the stack is removed so as to recover the thermoplastic elastomer-composite assembly thus produced.

Claims (12)

1. Method for producing a welded structural link between a thermoplastic matrix composite material and an elastomer, comprising the following operations:

   a first operation of functionalising the elastomeric material by incorporating into the green elastomeric material a given proportion of powder of a thermoplastic material, the functionalising being carried out by forming a thin layer (24) of green elastomeric material integrating a proportion of thermoplastic material powder and melting of said layer with a main layer (25) of elastomeric material during an operation of pressure-vulcanising said elastomeric material;

   a second welding operation per se, during which the welding of the thermoplastic composite material to the functionalised layer of the elastomeric material is carried out.
2. Method according to claim 1, characterised in that the operation of elaborating the functionalised elastomer itself comprises several steps:

   a preliminary step A) of cleaning the various portions of a vulcanising mould (21, 211);

   a first step B) during which a thin layer (24) of a pre-functionalised green elastomer is prepared by incorporating, homogeneously into this layer of elastomer a given proportion of thermoplastic material powder;

   a second step C) during which the thin layer of pre-functionalised green elastomer is applied to the surface of the elastomeric material (25);

   a third step D) during which the pressure-vulcanising of the elastomeric material is carried out; the pressure applied being determined in such a way that the thin layer (24) of pre-functionalised green elastomer is incorporated, at least on the surface, into the main layer (25) of elastomeric material during the vulcanising process.
3. Method according to one of claims 1 or 2, characterised in that the thermoplastic material incorporated into the thin layer (24) of elastomeric material is chosen in such a way as to be able to be welded to the thermoplastic material forming the matrix of the composite material and to have good compatibility with the elastomeric material.
4. Method according to claim 3, characterised in that the thermoplastic material incorporated into the thin layer (24) of elastomeric material is identical to the thermoplastic material forming the matrix of the composite material.
5. Method according to any of claims 1 to 3, characterised in that, the composite material being a carbon composite/polyetheretherketone and the elastomeric material being of the HNBR type, the thermoplastic material incorporated into the thin layer of elastomeric material is a polyetherimide.
6. Method according to claim 5, characterised in that the thermoplastic material is incorporated into elastomeric material in the form of particles with a diameter between 20 µm and 60 µm, in a proportion between 10 % and 25 % of the mixture by weight.
7. Method according to any of the preceding claims, characterised in that the welding operation consists in heating the contact surfaces of the two materials to be welded by interposing between these two surfaces a metal fabric (35) that acts as a heating resistance, the metal fabric being itself impregnated with thermoplastic material.
8. Method according to claim 7, characterised in that the welding operation is preceded by a preliminary operation I) of preparing surfaces of the materials to be assembled, this operation able to consist, according to the condition of these surfaces, either in a simple degreasing using a suitable solvent, or in a fine sanding of the functionalised surface of the element made of elastomer, followed by a cleaning of the surfaces with the same solvent.
9. Method according to any of the preceding claims 1 to 3 or 5 to 8, characterised in that, the composite material being a carbon composite/polyetheretherketone and the elastomeric material being of the HNBR type, the step C) of elaborating per se of the functionalised elastomer comprises the following operations:
   a first operation of setting in place, on the lower plateau (21) of the vulcanising mould, the following elements:

   two superimposed layers (22, 23) of Teflon-coated fibreglass,

   a fold of green elastomeric material (24) wherein polyetherimide powder has been incorporated,

   the folds of the green non-vulcanised elastomeric material (25),

   a set of edging shims (26, 27),

   two superimposed layers (28, 29) of Teflon-coated fibreglass,

   the whole being covered by the upper plateau (211) of the vulcanising mould;

   a second operation of setting in place the stack formed on the plateau of a heating press preheated to a temperature θ₂ of 140 °C;

   a third operation of hot pressing of the stack, during which the suitable nominal pressure cycle is applied to the elastomer in question;

   a fourth operation during which the mould is removed from the press while the latter maintains the temperature θ₂ of 140 °C, the functionalised elastomer is released and the latter is allowed to cool to ambient temperature.
10. Method according to claim 9, characterised in that the pressing cycle of the third operation comprises:

    a phase of a progressive rising in temperature until a high temperature θ₁ of 230 °C with a gradient of 2.5 °C/min,

    a phase of maintaining at the temperature θ₁ for 10 minutes,

    a phase of lowering the temperature to the temperature θ₂ of 140 °C according to a gradient of 2.5 °C/min.
11. Method according to any of the preceding claims, characterised in that, the composite material being a carbon composite/polyetheretherketone and the elastomeric material being of the HNBR type, the welding operation per se comprises the following steps:
    a first step of setting in place during which the following elements are arranged mainly, in order, on a plate (31) of thermal insulating material:

    a first film (32) made of heat-resistant polyimide,

    the functionalised elastomeric material (33),

    a first polyetherimide film (34),

    a metal fabric (35) pre-impregnated with polyetherimide,

    a second polyetherimide film (36),

    the thermoplastic composite material (36),

    a second polyimide film (37),

    a layer of thermal insulation (38),

    a fibreglass (311);

    a second step during which a bladder is vacuum-produced with a polyimide film (312) arranged in such a way as to allow the metal fabric (35) to exit, the seal of said bladder being provided by means of high-temperature mastic;

    a third step during which the bladder (312) is placed in a vacuum, an electrical power supply unit is connected on the metal fabric (35) and various values of intensity are applied according to a suitable cycle;

    a fourth step during which the polyimide film (312) used as a vacuum pack is removed and the stack is disassembled.
12. Method according to claim 11, characterised in that during the third step a current of 15.6 amperes is applied on the metal fabric (35) for 200 seconds then a current of 10 amperes for 100 seconds.

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